The present invention relates to a temperature-compensated piezoelectric oscillator which oscillates a constant output frequency regardless of variations in ambient temperature.
FIG. 2 shows a conventional digital temperature-compensated piezoelectric oscillator (microcomputer-controlled piezoelectric oscillator). This temperature-compensated piezoelectric oscillator comprises a temperature sensor 9, an A/D converter 5 for converting an analog output from the temperature sensor 9 into a digital code to output it, a microcomputer circuit 6 and a memory circuit 7 which receive the digital code output from the A/D converter 5, a D/A convertor 8 for converting an output digital code from the microcomputer circuit 6 into an analog voltage to output it, and a voltage-controlled piezoelectric oscillator 1 for receiving the analog voltage output from the D/A convertor 8.
In the temperature-compensated piezoelectric oscillator having this arrangement, the temperature sensor 9 detects an ambient temperature T of the voltage-controlled piezoelectric oscillator 1 as an analog voltage. The A/D converter 5 converts the detected ambient temperature T into a digital code to output it to the microcomputer circuit 6 and the memory circuit 7. The microcomputer circuit 6 calculates compensation data for the ambient temperature T at that time on the basis of a program and constant which are prestored in the memory circuit 7 to compensate the frequency/temperature characteristics of the voltage-controlled piezoelectric oscillator 1. The output digital code is supplied to the D/A convertor 8. The D/A convertor 8 converts the output digital code from the microcomputer circuit 6 into an analog voltage to supply it to the voltage-controlled piezoelectric oscillator 1.
With this arrangement, an output frequency F from the voltage-controlled piezoelectric oscillator 1 can always be kept constant regardless of a change in ambient temperature T.
In this conventional temperature-compensated piezoelectric oscillator, however, when the ambient temperature T abruptly changes, a temperature difference occurs between a piezoelectric element in the voltage-controlled piezoelectric oscillator 1 and the temperature sensor 9. For this reason, accurate temperature compensation is not performed to degrade frequency stability.